JPH07115185A - Electrode of semiconductor - Google Patents

Abstract

PURPOSE:To improve the solderability and ohmic properties of the ohmic electrode of a compound semiconductor such as a GaAs semiconductor. CONSTITUTION:An AuGeNi layer 2, an Mo layer 5, an Mo oxide layer 6, an Mo layer 7 an Ni layer 8 and an Au layer 9 are successively formed on a GaAs semiconductor 1. The Mo oxide layer 6 blocks the diffusion of Ni and Ge. As a result, the deterioration of the ohmic properties and solderability of the ohmic electrode can be avoided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode of a semiconductor such as an n-type 3-5 group compound semiconductor.

[0002]

2. Description of the Related Art Many methods for forming an ohmic electrode having a small contact resistance on GaAs which is a semiconductor have been proposed. Among these electrode forming methods, the most widely used method for n-type GaAs is
AuGeNi method. This method uses Ge on GaAs.
Is vacuum-deposited on the AuGe film.
After i is vapor-deposited and Au is further vapor-deposited on Ni in some cases, heat treatment (alloying heat treatment) is performed for 10 seconds to several minutes at a temperature equal to or higher than the melting point (356 ° C.) of AuGe. The ohmic contact metal layer 2 is formed on the GaAs semiconductor 1 as shown in FIG. By the way,
In the evaporated film of AuGe and Ni in the AuGeNi method,
The total thickness is 100 to 250 nm, and the AuGe film 1
It is said that it is preferable that the Ni film has a heat of about 28 nm with respect to 00 nm. Further, instead of separately depositing the AuGe film and the Ni film, Au containing Ge and Ni is vapor-deposited at one time to form an AuGeNi film, and the melting point of AuGe (356
There is also a method of forming a metal layer for ohmic contact by performing heat treatment (alloying heat treatment) at a temperature of 10 ° C. or higher for 10 seconds to several minutes.

[0003]

When mounting a chip, the ohmic electrode thus formed is soldered to a lead frame with a solder containing PbSn as a main component, and the AuGeNi electrode is mainly composed of Au. Therefore, the solder is easily eaten, that is, the AuGeNi deposited film diffuses into Pb and Sn in the solder. Since the solder is not directly and strongly adhered to the semiconductor chip, when AuGeNi is eroded by the solder, a defective electrical connection of the semiconductor chip and / or a defective heat dissipation occurs. To solve the above problem, FIG.
As shown in, the Ni layer 3 and the Au layer 4 may be sequentially provided on the AuGeNi layer 2. With this structure, even if the uppermost Au layer 4 melts into the solder, the Ni layer 3
Does not dissolve, so that the ohmic electrode peeling phenomenon does not occur. However, the Ni of the Ni layer 3 is changed to the AuGeNi metal layer 2
And diffuses into the GaAs semiconductor 1 through the through hole, resulting in a decrease in ohmic property.

Therefore, an object of the present invention is to provide a semiconductor electrode capable of maintaining good ohmic contact and solderability.

[0005]

The present invention for achieving the above object provides an ohmic contact metal layer formed on a surface of a semiconductor, and a molybdenum oxide layer formed on the ohmic contact metal layer. The present invention relates to a semiconductor electrode including a metal layer having good solderability formed on the molybdenum oxide layer. Note that claim 2
It is desirable to provide a molybdenum layer between the molybdenum oxide layer and the ohmic contact metal layer, as shown in FIG. Further, as described in claim 3, it is desirable to provide a molybdenum layer between the molybdenum oxide layer and the metal layer having good solderability. Further, as described in claim 4, it is preferable that the semiconductor is a 3-5 group compound semiconductor such as GaAs and the ohmic contact metal layer is an AuGeNi layer. Further, as described in claim 5, it is desirable that the metal layer having good solderability is composed of a Ni layer and an Au layer. Further, as described in claim 6, it is desirable that the oxygen content of the molybdenum oxide is 5 to 60 atomic%.

[0006]

The molybdenum oxide layer according to the present invention prevents the metal component of the ohmic contact metal layer from migrating to the side of the metal layer having good solderability, and the metal component of the metal layer having good solderability. To the ohmic contact metal layer side. Therefore, it is possible to provide an electrode having both good ohmic properties and solderability. Further, when the molybdenum layer is provided according to the second aspect, the bond between the molybdenum oxide and the ohmic contact metal layer becomes strong. When the molybdenum layer is provided according to the third aspect, the bond between the molybdenum oxide layer and the metal layer having good solderability becomes strong. As described in claim 4, when the ohmic contact metal layer made of the AuGeNi layer is provided on the 3-5 group compound semiconductor, a good ohmic electrode can be obtained. As shown in claim 5, N
Providing a metal layer composed of the i layer and the Au layer with good solderability makes it possible to achieve good solder connection. Further, by setting the oxygen content of the molybdenum oxide layer to 5 to 60 atomic%, it is possible to prevent a significant decrease in bond strength between the layers and prevent migration (diffusion) of metal.

[0007]

EXAMPLE Next, the electrode structure of a GaAs semiconductor device according to an example of the present invention will be described with reference to FIG. First, Au containing Ge and Ni was vacuum-deposited to a thickness of 200 nm on an n-type GaAs substrate 1 which is a compound semiconductor to form AuG.
The eNi layer 2 is formed. Next, Mo (molybdenum) is vapor-deposited on the AuGeNi layer 2 to form a Mo layer having a thickness of 200 nm. Then, O ₂ gas was introduced into the vacuum vapor deposition apparatus in the range of 5 × 10 ⁻⁵ Torr to 1 × 10 ⁻² Torr, and about 3
Hold for minutes to oxidize the surface of Mo. As a result, the first Mo layer 5 and the Mo oxide layer 6 shown in FIG. 3 are obtained. It is desirable that the oxygen content of the Mo oxide layer 6 be within the range of 5 to 60 atomic%. Next, Mo is evaporated again to form a second Mo layer 7 on the Mo oxide layer 6 having a thickness of 100 nm.

Next, a Ni layer 8 having a thickness of 500 nm is formed on the second Mo layer 7 by vacuum vapor deposition of Ni (nickel), and further a thickness of 200 nm is deposited by vapor deposition of Au (gold).
Au layer 9 is formed on the Ni layer 8. Ni layer 8 and A
The u layer 9 functions as a metal layer having good solderability.

Next, the metal layer on which each metal layer is formed is
_{2 In a} (non-oxidizing atmosphere), heat treatment (alloying heat treatment) is performed for 5 minutes at a temperature (eg, 380 ° C.) higher than the melting point of AuGe. By this alloying heat treatment, the AuGeNi layer is alloyed with GaAs to obtain an ohmic contact metal layer having a small contact resistance. This contact resistance is, for example, about 1 × 10 ⁻⁵ Ωcm ² when the impurity concentration of n-type GaAs is 1 × 10 ¹⁸ cm ⁻³ .

The Mo oxide layer 6 prevents Ni of the Ni layer 8 as a metal layer having good solderability from diffusing to the AuGeNi layer 2 side, and Ge in the AuGeNi layer 2 as an ohmic contact metal layer. Is Ni layer 8 and A
It is prevented from diffusing to the u layer 9 side. Therefore, when the lead member is connected to the electrode by the solder (PbSn), Ge does not diffuse into the Au layer 9 and the Ni layer 8 and the solder wettability does not deteriorate. Further, the Ni of the Ni layer 8 is AuGe.
It does not diffuse to the Ni layer 2 side to deteriorate the ohmic property.

Although Mo has almost no function of preventing diffusion of Ni and Ge, Mo oxide has the above-mentioned function. The amount of oxygen in the Mo oxide layer 6 is preferably as large as possible in order to prevent Ni and Ge from diffusing, but in order to keep a large bonding strength with an adjacent layer and to suppress an increase in electric resistance,
It is desirable to set it in the range of 60 atomic%. Also,
The thickness of the Mo oxide layer 6 is preferably as thick as possible in terms of preventing diffusion of Ni and Ge, but in order to prevent an increase in electric resistance, when the oxygen amount is 60 atomic%, the thickness is in the range of 20 to 80 angstroms. When the oxygen amount is 5 atomic%, it is desirable to set it in the range of 0.1 to 0.5 μm. After all, it is desirable that the thickness of the Mo oxide layer 6 be within the range of 20 Å to 0.5 μm.

In the electrode structure shown in FIG. 3, first and second Mo layers 5 and 7 are provided on both sides of the Mo oxide layer 6. Mo
The layers 5 and 7 are relatively strongly bonded to the Mo oxide layer 6 and also strongly bonded to the AuGeNi layer 2 and the Ni layer 8. Therefore, it is possible to provide an electrode in which the peeling phenomenon does not easily occur despite the presence of the Mo oxide layer 6.

[0013]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) As shown in FIG. 4, from the electrode of FIG.
It is possible to have a structure in which the layer 7 is omitted. (2) As shown in FIG. 5, from the electrode of FIG.
It is possible to have a structure in which the layer 5 is omitted. (3) Instead of the Ni layer 8, a Cu (copper) layer can be provided as a metal layer having good solderability. In addition, the Au layer 9
In place of the above, an Ag (silver) layer may be provided, and in some cases, the Au layer 9 may be omitted. (4) Instead of introducing O ₂ gas when forming the Mo oxide layer 6, another oxidizing atmosphere containing oxygen (for example, air)
Can be (5) The semiconductor is not limited to GaAs, but GaAs
It may be a 3-5 group compound semiconductor such as P, GaAlAs, or GaP. (6) The ohmic contact metal layer 2 is made of AuGeNi.
Other metal layers can be used. Also, AuGeNi
The layer may be formed by a method of depositing Au containing Ge and then depositing Ni.

[Brief description of drawings]

FIG. 1 is a front view showing a conventional electrode structure.

FIG. 2 is a front view showing another conventional electrode structure.

FIG. 3 is a front view showing an electrode structure according to an embodiment of the present invention.

FIG. 4 is a front view showing an electrode structure of a modified example of the present invention.

FIG. 5 is a front view showing an electrode structure of another modification of the present invention.

[Explanation of symbols]

 1 GaAs semiconductor 2 AuGeNi layer 5, 7 Mo layer 6 Mo oxide layer

Claims (6)

[Claims] 1. An ohmic contact metal layer formed on a surface of a semiconductor, a molybdenum oxide layer formed on the ohmic contact metal layer, and a solderability layer formed on the molybdenum oxide layer. Semiconductor electrode consisting of a good metal layer. 2. The semiconductor electrode according to claim 1, further comprising a molybdenum layer between the molybdenum oxide layer and the ohmic contact metal layer. 3. The semiconductor electrode according to claim 1, further comprising a molybdenum layer between the molybdenum oxide layer and the metal layer having good solderability. 4. The semiconductor electrode according to claim 1, 2 or 3, wherein the semiconductor is a Group 3-5 compound semiconductor and the ohmic contact metal layer is an AuGeNi layer. 5. The semiconductor electrode according to claim 1, wherein the metal layer having good solderability is a Ni layer and an Au layer formed on the Ni layer. 6. The molybdenum oxide layer has an oxygen content of 5
The electrode of the semiconductor according to claim 1, which is a molybdenum oxide layer of -60 atomic%.